DESCRIPTION: This is a proposal which outlines approaches for the development of potent and selective somatostatin (also known as somatotropin release inhibiting factor or SRIF) agonists and antagonist to each of the five recently discovered and cloned receptor subtypes SSTR1, SSTR2, SSTR3, SSTR4 and SSTR5. This area of research is highly desired since selective and potent SRIF analogs are needed as tools to unravel multiple SRIF actions and SRIF involvement in the control of neurotransmission, glandular secretion, smooth muscle contractility and cell proliferation.